Yesterday morning, a teenager walked into the cafeteria at Chardon High School in Chardon, Ohio and opened fire, apparently targeting a particular group of students. One died immediately, another at the hospital, and several others were seriously wounded.

The news coverage about this attack has repeatedly mentioned that the school had practiced for this kind of an event. Students say they didn't know whether this was a drill or the real deal. Teachers knew how to lock down their rooms. There's no way to know how many lives were saved by this training, or whether the shooter never intended to kill more people than he did.

The news coverage also mentions that parents outside the school were alerted to the situation through text messages from their kids, and kids inside the school spread information among one another via text. Since the Columbine attacks almost 13 years ago, most states and most schools have allowed cell phones in the classroom for just this reason -- to allow kids to communicate in a life-threatening emergency.

So, here's what's bugging me. If a school is in lockdown -- if they are trained to be in lockdown -- one of the things they should know is that, during a lockdown, you turn off your cell phone.

This may seem counterintuitive. After all, isn't the entire point of having a cell phone so you can communicate in an emergency? But during a lockdown you are locking yourself inside a dark room and hiding. You are trying not to be noticed, in case the gunman comes looking for more victims in your general direction. You are silent.

And if you are silent, that means turning off your cell phone. A ringing phone -- or even the sound of one vibrating -- can be the thing that tips off the bad guys to where you are and makes you a target. And you know that if the word gets out to parents that there's a gunman in the building, phones are going to start ringing. In a situation where a shooter may be looking to shoot anyone he can easily find, you just made yourself easy to find.

When I have been at schools that practiced lockdowns, the staff always are aware that getting kids to turn off their cell phones is going to be the hardest thing because it is so counterintuitive. But it has to be done.

There is a place for cell phones in these situations. A quick 911 call can mean the difference between life and death. But then the phone goes off. While contacting your parents or your friends may feel reassuring, it's not nearly as useful as staying alive.